Heaters heretofore manufactured for use in solder pots and the like consisted of a conventional tubular heater and an iron sheath cast about that portion of the tubular heater that is subject to contact with the molten metal to protect the sheath of the tubular heater from attack by the molten metal.
In this form of manufacture the tubular heater had to first be sent to the desired configuration which, in the case of the over-the-side heaters, consisted of an upper horizontal portion to be disposed over the side wall of the pot, and vertical and lower horizontal portions to be disposed within the pot.
Casting a protective iron sheath about the tubular heater involved considerable expense, both in equipment and labor, especially when the protective sheath was cast about a tubular heater that had been bent to a shape as disclosed above. First of all, the mold in which such casting operation was to be conducted was necessarily expensive because of the curvilinear cavity required. However, perhaps the most important disadvantage of the casting operation was the difficulty in maintaining the tubular heater in centered relation during the casting and solidifying operations. Frequently, the movement of the molten cast metal into the mold would shift the tubular heater off center or even the weight of the tubular heater, during the time the cast metal was solidifying would cause the tubular heater to sag to an off center condition.
When the tubular heater is in an off center position, the utility of the final product is severely affected because the protection shield around the heater is only as good as its cross sectional thickness, and if it is of nonuniform thickness, the protection will be only as good as the thinnest cross section.
Some prior art patents, such as U.S. Pat. No. 2,036,788, issued to C. C. Abbott on Apr. 7, 1936, and U.S. Pat. No. 2,987,689, issued to T. H. Lennox on June 6, 1961, disclose a tubular heater with an extra outer sheath, but these heaters would be unsuitable for molten metal pot heating applications since the molten metal would soon eat through the outer sheath and then through the inner sheath, and thereby cause destruction of the heater.
Our invention provides heavy wall protection for a tubular heater, without the expense and disadvantages of the molding operation heretofore described. Low cost manufacture is effected since a standard, rectilinear tubular unit may be used, this unit being slipped into the center opening in a thick wall pipe or tube which is substantially coextensive with the tubular unit. The pipe is side pressed or rolled, or by any other suitable means is reduced in diameter to thereby tightly fit about the tubular unit. Thereafter, the assembly may be bent to any desired configuration in a pipe bender of suitable construction, and the assembly is ready for use.